As Harold mentioned, the first thing to do is forget about Rail Europe as it's not the most reliable place to check rail schedules in Europe.
It appears that 28 May is a particularly bad day to be travelling from the south of France to Paris, as I also checked trains from Nice to Paris and most of those are also sold out. As it's a Sunday, the weekend travellers are probably heading home for work the next day.
I checked Trainline again, and there still seems to be seats available on the 13:40 departure from Marseilles (2nd class, €120 PP), but I expect those will probably be gone by the end of today. That leaves two options.....
- get a hotel in Marseilles for one night and travel by train the next day.
- take a flight from Marseilles to Paris. Air France is probably your best bet, although if you travelled to Nice you could also use easyJet. I checked flights from Nice and the cost is unusually high that day, probably due to the fact that the cheaper seats are already sold out, and also there may be higher demand that day.
If you were thinking of driving, note that you will require an International Driver's Permit, which is used in conjunction with your home D.L. OR a certified copy of the terms of your home D.L in French. You'll also have to budget for tolls on the motorways. For a trip of that distance, driving would not be my choice.